Didymo has been recently confirmed in the Upper Delaware System. But an article says it was seen there in 1916. It may not thrive and become a major problem everywhere it's found. I hope not. There is still not enough known about this yet.

UPPER DELAWARE REGION ? Don?t give ?rock snot? a ride, urged the New York State Department of Environmental Conservation (DEC) recently, following the discovery of the aquatic nuisance algae, Didymo, in the Delaware River. The presence of Didymo has now been confirmed in the mainstem of the Delaware, as well as in the East and West branches. River recreationists are being asked to take precautions against transporting it to new locations.

Didymo (Didymosphenia geminata), an invasive species in New York, was discovered in a section of the Batten Kill in Washington County early this summer. It has also been found in Vermont, Quebec and several western states.

The unsightly algae forms mats in rivers and then becomes a barrier to native organisms such as caddis, mayflies and stoneflies. The decline in insect populations can cause a corresponding decline in fish populations. Didymo can also affect stream ecosystem functions and may alter the foodweb structure and river hydraulics.

Getting answers

It is unclear whether or not the pesky algae will thrive in the mighty waterway, since traditionally Didymo prefers cold waters with low nutrient levels. For unknown reasons, the algae appears to be adapting. ?It?s a potential concern in that it can form these dense mats that exclude some native benthic invertebrates,? said Don Hamilton, natural resource specialist with the National Park Service, Upper Delaware Scenic and Recreational River (NPS UPDE). ?But whether or not it?s ever going to develop here is unknown.?

In an effort to learn more about the single-celled diatom, Hamilton and Richard Evans, an ecologist with the NPS Delaware Water Gap National Recreation Area, have submitted a technical assistance grant request to increase the knowledge base about Didymo and develop a possible strategy for dealing with it.

?It?s part of an effort to better understand what causes it to occasionally bloom and develop an approach to managing it. To do this, we need to know what some of the environmental variables might be affecting these blooms,? said Hamilton. ?We don?t really have a good understanding of what causes Didymo to bloom in a particular location when it does, nor do we know enough about its natural distribution. Are we seeing new introductions and expansion of its range, or changes in its extracellular growth and formation of dense mats on stream substrate due to environmental conditions?? asked Hamilton.

The answers to such questions are sought after by others studying Didymo. Dr. Martina Potapova is a research scientist at the Academy of Natural Sciences in Philadelphia, PA, specializing in riverine algae and their uses as environmental indicators. According to Potapova, this is not the first time that Didymo has been documented in the Delaware. ?There was a record of Didymosphenia in the Delaware River in 1916, so it is definitely not a new arrival,? she noted. ?It is actually a species commonly found in colder and cleaner rivers, so we cannot say that its presence indicates some sort of pollution.

?On the other hand, the recent findings of big masses of Didymo in western streams, including those polluted by nutrients, are telling us that something might have happened to this species,? said Potapova. ?There are only hypotheses about what could have caused the Didymo to change its ecology and to become a ?nuisance? species. Perhaps it is a case of a rapid evolutionary change, when a random mutation was advantageous because it allowed the species to thrive in polluted rivers, and this mutation was supported by natural selection, perhaps something else.?